The present invention relates generally to field devices for process measurement and control. Specifically, the invention concerns input signal conversion electronics for a discrete input transmitter.
Field devices cover a broad range of process management devices that measure and control parameters such as pressure, temperature, and flow rate. A transmitter is a type of field device in communication with a transducer, for example a sensor or an actuator, and also in communication with a remote control or monitoring device, such as a computer. The output signal of a sensor, for example, is generally insufficient to communicate effectively with a remote control or monitoring device. A transmitter bridges the gap by receiving the communication from the sensor, converting the signal to a form more effective for longer distance communication, for example a modulated 4-20 mA current loop signal, or a wireless protocol signal, and transmitting the converted signal over a current loop or through a wireless field device network to the remote control or monitoring device.
Wireless field devices are becoming prevalent in industrial applications. As components of wireless field device networks, wireless devices extend the reach of control or process monitoring systems beyond that of wired devices to locations where wiring may be difficult and expensive to provide. The use of lower power electronics and RF radios is essential for wireless network systems designed for transducer-based applications, such as a wireless field device network. Many devices in the network must be locally-powered because power utilities, such as 120V AC utilities or powered data buses, are not located nearby or are not allowed into hazardous locations where instrumentation and transducers must be located without incurring great installation expense. A common characteristic of local power sources is their limited power capacity, either stored, as in the case of a long-life battery, or produced, as in the case of a solar panel. Batteries are expected to last more than five years and preferably last as long as the life of the product.
There is a need for industrial wireless transmitters with electronics designed for low power consumption and able to communicate parameters such as pressure, temperature, and flow for process monitoring and control applications.